1. Field of the Invention
The present invention relates to a fuel supply apparatus for a direct injection gasoline internal combustion engine. In particular the invention relates to techniques with a direct injection gasoline internal combustion engine having direct injection of fuel into the combustion chamber, for managing at start up, air and fuel vapor which have mixed in the fuel piping when the engine is stopped.
2. Related Art of the Invention
Heretofore there is known a fuel supply apparatus for a direct injection gasoline internal combustion engine, which comprises; a fuel injection valve for injecting fuel directly into the combustion chamber, a high pressure fuel pump for supplying fuel to the fuel injection valve, a low pressure fuel pump for supplying fuel to the high pressure fuel pump, a low pressure pressure regulator for adjusting the pressure in a low pressure fuel system between the low pressure fuel pump and the high pressure fuel pump to a predetermined low pressure, and a high pressure pressure regulator for adjusting the pressure in a high pressure fuel system downstream of the high pressure fuel pump to a predetermined high pressure.
Furthermore, with the fuel supply apparatus for a direct injection gasoline internal combustion engine constructed as described above, as a method for discharging the fuel vapor and air inside the fuel piping to ensure startability, there is an arrangement as disclosed in Japanese Unexamined Patent Publication No. 7-77119.
With the method disclosed in the above publication, a branch path which bypasses the high pressure pressure regulator is provided for returning fuel which has been supplied from the high pressure fuel pump directly to the fuel tank, and an open/close valve is disposed in the branch path so that by opening the open/close valve at the time of start up, fuel in the high pressure fuel piping is discharged together with vapor.
With the abovementioned conventional method however, the construction is such that the pressure adjustment by the low pressure pressure regulator is normally carried out also when the fuel in the high pressure fuel system is being returned directly to the fuel tank. Therefore, the fuel which is returned to the fuel tank from the low pressure pressure regulator of the fuel which is pumped from the low pressure fuel pump does not contribute to the expulsion of fuel in the high pressure fuel system. As a result, there is the problem that the fuel in the high pressure fuel system cannot be discharged with good efficiency.
Furthermore, with the conventional method, when the open/close valve is opened so that the fuel is returned directly to the fuel tank from the high pressure fuel system, then since pressure adjustment in the high pressure fuel system is not carried out at all, the fuel pressure changes so that the injection quantity becomes unstable, with the problem that controllability of the air/fuel ratio at the time of start up is compromised.